Dynamoelectric machines, such as high speed induction motors often find uses indoors or outdoors in environments where they need to be protected from dripping fluids, rain, snow, and other forms of precipitation, as well as from dirt, dust or other particles contained in the atmosphere, all of which can interfere with the proper functioning of the motor. As a result, various housing designs have been developed to protect the moving parts inside of the yoke from the weather, while permitting adequate intake and exhaust of air to cool the machine or motor. U.S. Pat. Nos. 2,777,079 and 4,119,873 discuss dynamoelectric machines such as electric motors having a top cover to render the machine suitable for outdoor use.
One series of two pole high speed induction motors has a squarish motor bearing housing or yoke with a flat upper surface. A box-shaped cover fits on the housing and permits intake and exhaust of coolant while substantially preventing entry of dripping fluids, rain, dust, airborne dirt and other particles. The use of covers introduces vibration problems which may be exacerbated because the cover may create a resonant structure amplifying vibration of the motor. Introduction of resilient washers, however, creates a space through which air and unwanted dirt and precipitation may flow, thereby disrupting the air flow path and interfering with the weather resistance provided by the cover.
U.S. Pat. Nos. 4,007,388, 4,425,813, and 5,026,476 all seem directed to vibration problems encountered with rotary machines and electrodynamic machines such as electric motors. None of the foregoing references discusses a complete solution to the problem of efficient cooling and weather resistance of electrical apparatus combined with effective suppression of the vibration generated by the apparatus and amplified by its protective cover.